Denitrification by heterotrophic bacteria during activated sludge treatment

Abstract

It is generally accepted that Pseudomonas spp. are the predominant heterotrophic bacteria involved in denitrification during activated sludge treatment. However, uncertainty still exists regarding other bacteria involved. This study therefore aimed to determine which heterotrophic bacteria present in mixed liquor samples from a biological nutrient removal process are responsible for denitrification as well as to establish the extent to which these bacteria contribute to nitrate and nitrite reduction under anoxic conditions. Heterotrophic bacteria were isolated, using plating techniques, from the anoxic zone of the Darvill activated sludge process and assessed for nitrate and nitrite reduction under anoxic conditions. Results show a significant involvement of Pseudomonas spp. in nitrate and nitrite reduction. It was also found that many other heterotrophic bacteria are involved to some extent in denitrification, most of which were found to be incomplete denitrifiers only capable of reducing nitrates to nitrites with no further reduction of the nitrites produced.

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